A French soldier patrolling a business neighbourhood west of Paris has been stabbed in the neck by a man who fled the scene.

The 23-year-old was patrolling in uniform with two other soldiers as part of France's anti-terrorism surveillance plan in La Defense when he was approached from behind around 6pm on Saturday (local time) and attacked with a knife or a box-cutter.

While anti-terrorist investigators were probing the incident President Francois Hollande said "at this stage" there was no apparent link between the attack in Paris and a murder of a soldier in London this week.

"We still don't know the exact circumstances of the attack or the identity of the attacker, but we are exploring all options," he said.

Mr Hollande said police were hunting for the perpetrator but did not provide any details about his identity or any possible motivation for the attack.

A police union spokesman said surveillance footage of the attacker showed him as tall and bearded, aged about 35, possibly of North African origin and wearing a white Arab-style tunic.

Three days after a British soldier was killed in a London street by two men who said they acted to avenge violence against Muslims, the attack near Paris raised questions about a possible copycat attempt.

Interior minister Manuel Valls noted the similarity in an interview on French TV, saying the attacker was clearly trying to murder his victim, but he added it was too early to offer any theories.

"Let's be prudent for now," Mr Valls said of the attacker's identity and motivations.

"Everything is being done to arrest this individual."

Defence minister Jean-Yves Le Drian told journalists near the site of the attack: "The soldier was attacked because he is a soldier."

Soldier treated in military hospital

Pierre-Andre Peyvel, police prefect for the Hauts-de-Seine area west of Paris, said the soldier lost a considerable amount of blood but would survive, and was being treated in a nearby military hospital. He was not named.

Witnesses near the train station where the attack occurred gave conflicting descriptions of the fleeing suspect.

One asserted on television he saw two men fleeing, while another said the scene was too confused to tell.

Mr Peyvel declined to confirm or deny any description and said further details would be forthcoming.

France is on high alert for attacks by Islamist militants following its military intervention in Mali in January, which prompted threats against French interests from AQIM, the North African wing of Al Qaeda.

The latest warning was published on YouTube a few weeks before armed gunmen this week attacked a military base and a French uranium extraction site in the central African state of Niger, killing 24 soldiers and one civilian.

Mr Valls said France would retain its current terror alert level at "red, reinforced", one step down from "scarlet", which is only activated in case of a serious and confirmed attack.